Black men have a higher prevalence of cognitive decline, dementia, and Alzheimer?s disease (AD) than their educational counterparts of other races. While these differences are well documented, little is known about the possible mechanisms that undergird these disparities. Cognitive decline, dementia, and AD may be the consequence of genetic risk triggered by environmental insult. Unique and compounded environmental exposures may lead to the poor cognition and increased risk of dementia and AD among Black men. The prevention of cognitive decline and dementia through the identification of modifiable risk factors has garnered increased public health interest. Mechanisms through which environmental exposures have been proposed to affect health outcomes are through inflammation, oxidative stress, and gene methylation. Sources of both physical and environmental factors ? at the individual, community, and area-based levels ? may interact with biological and psychosocial characteristics, potentially increasing cumulative risk for various adverse health outcomes, including cardiovascular disease, diabetes, and mortality. Additionally, there is a growing body of literature suggesting that psychosocial stressors commonly associated with health disparities may amplify the effects of environmental exposures in more vulnerable populations. Although previous studies have examined ambient air pollution and cognitive impairment, they have often attempted to do so with small sample sizes, with little diversity, or using a cross-sectional design and have reported conflicting results. For this study, we will utilize longitudinal cohort data from Black men enrolled in the Health and Retirement Study (HRS) to classify subjects with probable dementia versus no dementia, AD diagnosis, and progressive cognitive decline. These data will be linked to hazardous air pollutant models based on geocoded addresses along with subject- level and area-based measurements of psychosocial stressors. We will then investigate the association between residential ambient air pollutant concentrations and age-adjusted incidence of cognitive impairment, dementia, and AD as well as rate of cognitive decline. We will also determine the associations between social inequalities related to income and education level and exposures to ambient air pollutants. Lastly, we will identify the role of psychosocial stressors in relation to ambient air pollutant exposures and risk of cognitive decline, dementia, and AD. The resulting findings from this ancillary study will be utilized to inform research objectives for subsequent grant submissions addressing unique risks for late-life cognitive impairment in Black men. Therefore, our research is ground-breaking from both a scientific and justice perspective and promises to generate new insights into the mechanisms of the disproportionate burden of illness in this particularly vulnerable demographic group. These results will help inform public health policy to reduce the substantial burden of cognitive decline in Black men and other high-risk populations.